Genomic Comparisons of Two Armillaria Species with Different Ecological Behaviors and Their Associated Soil Microbial Communities

Fire-associated microbial shifts in soils of western conifer forests with Armillaria root disease

Fires in coniferous forests throughout the northern United States alter ecosystem processes and ecological communities, including the diversity and composition of microbial communities living in the soil. In addition to its influence on ecosystem processes and functions, the soil microbiome can interact with soilborne pathogens to facilitate or suppress plant disease development. Altering the microbiome composition to promote taxa that inhibit pathogenic activity has been suggested as a management strategy for forest diseases, including Armillaria root disease caused by Armillaria solidipes, which causes growth loss and mortality of conifers. These forest ecosystems are experiencing increased wildfire burn severity that could influence A. solidipes activity and interactions of the soil microbiome with Armillaria root disease. In this research, we examine changes to the soil microbiome following three levels of burn severity in a coniferous forest in northern Idaho, United States, where Armillaria root disease is prevalent. We further determine how these changes correspond to the soil microbiomes associated with the pathogen A. solidipes, and a putatively beneficial species, A. altimontana. At 15-months post-fire, we found significant differences in richness and diversity between bacterial communities associated with unburned and burned areas, yet no significant changes to these metrics were found in fungal communities following fire. However, both bacterial and fungal communities showed compositional changes associated with burn severity, including microbial taxa with altered relative abundance. Further, significant differences in the relative abundance of certain microbial taxa in communities associated with the three burn severity levels overlapped with taxa associated with various Armillaria spp. Following severe burn, we observed a decreased relative abundance of beneficial ectomycorrhizal fungi associated with the microbial communities of A. altimontana, which may contribute to the antagonistic activity of this soil microbial community. Additionally, A. solidipes and associated microbial taxa were found to dominate following high-severity burns, suggesting that severe fires provide suitable environmental conditions for these species. Overall, our results suggest that shifts in the soil microbiome and an associated increase in the activity of A. solidipes following high-severity burns in similar conifer forests may result in priority areas for monitoring and proactive management of Armillaria root disease.

IMPORTANCE

With its influence on ecosystem processes and functions, the soil microbiome can interact with soilborne pathogens to facilitate or suppress plant disease development. These forest ecosystems are experiencing increased wildfire frequency and burn severity that could influence the fungal root pathogen, Armillaria solidipes, and interactions with the soil microbiome. We examined changes to the soil microbiome following three levels of burn severity, and examined how these changes correspond with A. solidipes, and a putatively beneficial species, A. altimontana. Following severe burn, there was a decreased relative abundance of ectomycorrhizal fungi associated A. altimontana. A. solidipes and associated microbial taxa dominated following high-severity burns, suggesting that severe fires provide suitable environmental conditions for these species. Our results suggest that shifts in the soil microbiome and an associated increase in the activity of A. solidipes following high-severity burns in conifer forests may result in priority areas for monitoring and proactive management of Armillaria root disease.

Less is more: A new strategy combining nanomaterials and PGPB to promote plant growth and phytoremediation in contaminated soil

Novel combination strategies of nanomaterials (NMs) and plant growth-promoting bacteria (PGPB) may facilitate soil remediation and plant growth. However, the efficiency of the NM-PGPB combination and interactions among NMs, PGPB, and plants are still largely unknown. We used multiwalled carbon nanotubes (MWCNTs) and zero-valent iron (nZVI) combined with Bacillus sp. PGP5 to enhance the phytoremediation efficiency of Solanum nigrum on heavy metal (HM)-contaminated soil. The NM-PGPB combination showed the best promoting effect on plant growth, which also had synergistic effects on the bioaccumulation of HMs in S. nigrum. The MWCNT-PGP5 combination increased the Cd, Pb, and Zn removal efficiency of S. nigrum by 62.03%, 69.44%, and 61.31%, respectively. The underlining causes of improved plant growth and phytoremediation by NMs-PGPB combination were further elucidated. NM application promoted PGPB survival in soil. Compared with each single application, the combined application minimized disturbance to plant transcription levels and rhizosphere microbial community, resulting in the best performance on soil remediation and plant growth. The NM-PGPB-induced changes in the microbial community and root gene expression were necessary for plant growth promotion. This work reveals the "less is more" advantage of the NM-PGPB combination in soil remediation, providing a new strategy for soil management.

The role of symbiotic fungi in the life cycle of Gastrodia elata Blume (Orchidaceae): a comprehensive review

Gastrodia elata Blume, a fully mycoheterotrophic perennial plant of the family Orchidaceae, is a traditional Chinese herb with medicinal and edible value. Interestingly, G. elata requires symbiotic relationships with Mycena and Armillaria strains for seed germination and plant growth, respectively. However, there is no comprehensive summary of the symbiotic mechanism between fungi and G. elata. Here, the colonization and digestion of hyphae, the bidirectional exchange of nutrients, the adaptation of fungi and G. elata to symbiosis, and the role of microorganisms and secondary metabolites in the symbiotic relationship between fungi and G. elata are summarized. We comprehensively and deeply analyzed the mechanism of symbiosis between G. elata and fungi from three perspectives: morphology, nutrition, and molecules. The aim of this review was to enrich the understanding of the mutualistic symbiosis mechanisms between plants and fungi and lay a theoretical foundation for the ecological cultivation of G. elata.

Armillaria altimontana in North America: Biology and Ecology

Armillaria altimontana is a fungus (Basidiomycota, Agaricomycetes, Agaricales, and Physalacriaceae) that is generally considered as a weak/opportunistic pathogen or saprophyte on many tree hosts. It widely occurs across the northwestern USA to southern British Columbia, Canada, but relatively little is known about its ecological role in the diverse forest ecosystems where it occurs. This review summarizes the biology and ecology of A. altimontana, including its identification, life cycle, distribution, host associations, and bioclimatic models under climate change.